﻿#region License
/*  YanYeovil
    Copyright (c) 2014, Alexey A. Popov
    All rights reserved.

    Redistribution and use in source and binary forms, with or without modification, are
    permitted provided that the following conditions are met:

    - Redistributions of source code must retain the above copyright notice, this list
      of conditions and the following disclaimer.

    - Redistributions in binary form must reproduce the above copyright notice, this list
      of conditions and the following disclaimer in the documentation and/or other materials
      provided with the distribution.

    - Neither the propertyName of the Alexey A. Popov nor the names of its contributors may be used to
      endorse or promote products derived from this software without specific prior written
      permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS *AS IS* AND ANY EXPRESS
    OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
    AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
    CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
    DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
    IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
    OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#endregion

using System;
using System.Collections.Generic;

namespace Pvax.Data
{
    /// <summary>
    /// Provides a default implementation of the <see cref="IEqualityComparer{TId}"/>
    /// interface.
    /// </summary>
    /// <typeparam name="TId">The <see cref="IId{TKey}"/> interface.</typeparam>
    /// <typeparam name="TKey">The primary key type.</typeparam>
    /// <remarks>
    /// This class uses only primary key values for comparison and hash code calculation.
    /// </remarks>
    public class DefaultPrimaryKeyComparer<TId, TKey>: IEqualityComparer<TId>
        where TId: IId<TKey>
    {
        #region IEqualityComparer<TId> Members

        /// <summary>
        /// Determines whether the specified objects are equal.
        /// </summary>
        /// <param name="x">The first object to compare.</param>
        /// <param name="y">The second object to compare.</param>
        /// <returns>
        /// <c>true</c> if the specified objects are equal; <c>false</c> otherwise.
        /// </returns>
        public bool Equals(TId x, TId y)
        {
            if(null == x)
                return null == y;
            return x.Id.Equals(y.Id);
        }

        /// <summary>
        /// Returns a hash code for the specified object.
        /// </summary>
        /// <param name="obj">
        /// The instance of the <see cref="IId{TKey}"/> for which a hash code is to be returned.
        /// </param>
        /// <returns>
        /// The hash code for the <paramref name="obj"/>.
        /// </returns>
        public int GetHashCode(TId obj)
        {
            if(null == obj)
                throw new ArgumentNullException("obj", Properties.Resources.ErrNullParam);
            return obj.Id.GetHashCode();
        }

        #endregion
    }
}
